Intumescent coating composition and articles coated therewith



Nov. 10, 1959 E. K. STILBERT, JR.. ETAL 2,912,394

INTUMESCENT COATING COMPOSITION AND ARTICLES comm THEREWITH Filed Dec.24, 1958 F/re rc/araan/ lh/umescen/ 600/171 ma/er/a/ INVENTORS. E/merS/f/ber/j Jr. Ira H. Cummings Gera/a E. 6/ock DYfiZ. g a

HTTORNEYS U it Pat fi pfi e INTUMESCENT COATING- COMPOSITION ANDARTICLES COATED THEREWITH Elmer K. Stilbert, Jr., Ira James Cummings,and Gerald E. Clock, Midland, Mich., assignors to The Dow ChemicalCompany, Midland, Mich., a corporation of Delaware Application December24, 1958, Serial No. 782,968

10 Claims. (Cl. 26017.4)

This invention concerns an improved intumescent coating compositions anda wall member, such as fiber-board, coated therewith.

This application is a continuation-in-part of US. Serial No. 594,204,filed June 27, 1956.

Intumescent coating compositions have b'een'applied in the past tocombustible materials such as fiber-board for protection against fire.Some of these compositions are disclosed in US. Patents 2,425,054,"2,523,626 and 2,566,964. All of these coating compositions depend onformaldehyde, or some other reactive material toform a resin which mayserve as a binding agent. The presence of reactive substances causesseveral disadvantages such as a narrow operative pH range and a shortwet stable life of the formulated compositions. coatings generallyexhibit poor resistance to. washing and scrubbing operations.

The provision of an intumescent fire-retardant coatin with improvedflexibility and resistance to washing and scrubbing operations is theprincipal object of this invention.

A further object is the provision of an'intumescent fire-retardantcoating composition based-on non-reactive materials.

Still another object is the provision of an intumescent coating with animproved wet storage life. I

Another object is to provide a fibrous wall member coated with ascrub-resistant, intumescent, fire-retardant coating.

The above and related objects are accomplished by this invention inwhich a combustible building material is provided with anabrasion-resistant, intumescent coating deposited from a 40 to 60percent aqueous dispersion of a mixture consisting of non-film formingintumescent solids and an aqueous, film-forming, latex-like dispersionof polystyrene. The non-film forming intumescent solids consist of afoam-forming substance or spumific, a non resinous carbon yieldingsubstance or carbonific, and an organic nitrogen compound.

Materials suitable as non-resinous carbonifics are carbohydrates,modified starches and similar substances, a

water dispersible protein such as gelatin or casein, or a polyhydriccompound from the class consisting of the hexitols, such as mannitol,the pentitols such as arabitol, or the mono-, or di-tetritols' such asmono and di-pentaerythritol. It is also possible to use a mixture of twoor more of the above-mentioned products. It is preferred to usepentaerythritol or the dimer of pentaerythritol, or mixtures of the twofor the non-resinous carbonific. Commonly the commercial grades ofmonopentaerythritol contain minor amounts of the dimer.

While an organic nitrogen compound is not entirely essential, improvedintumescence is obtained from a composition containing one. Aminocompounds such as dicyandiamide, urea, dimethyl urea, guanylureaphosphate, and glycine are suitable organic nitrogen compounds. Ofthese, urea or dicyandiamide are preferred as the organic nitrogencompound.

These previous At temperatures at or near the temperature of combustionof wood, the non-resinous carbonific and organic nitrogen compound incombination with a foam-producing agent, or spumific, forms a fireresistant carbonaceous foam. The spumifics that may be used in thisinvention are preferably monoammonium phosphate, diammonium phosphate,phosphoric acid, ammonium sulfate, sulfamic acid, ammonium sulfamate,ammonium bromide, sodium tungstate, or sodium borate.

The carbonific may be present in amounts of from 10 to 70 percent of theweight of the spumific, and preferably 35 to 45 percent. When starch isused as a part'of the carbonific, it is preferred to maintain the amountof starch at less than 15 percent of the weight of the spumific. Whenthe amount of starch used is appreciably above 15 percent, both theintumescent rating and the scrub resistance of the coatings isnoticeably de creased. The organic nitrogen compound may be present inamounts of from 0 to 55 percent of the weight of the: spumific, but thepreferred range is 5 to 20 percents The spumific should form about 30 topercent of the weight of the non-resinous intumescent solids. When morespumific is used, the walls of the heat-generated foam are fractured byexcessive gassing of the spumific. When the non-resinous carbonific ismore than the stated amount, insufficient spumific is present to formthe deep foam needed for insulating the combustible coated material.When an excess of the organic nitrogen compound is used, the amount ordegree of intumescence is again too low. The amounts that are to be usedin any given coating to provide the maximum intumescence may bedetermined by simple preliminary experiments.

Such compositions, when employed without further modification, lackresistance to abrasion. Therefore, a polymer latex ofpolystyrene,vusually of about 50 percent solids, is incorporated intothe coating compositionjas'a binder, so that the amount of the latexsolids in the composition is from 5 to 35 percent of the total solids,but preferably from 15 to 30 percent. As is known in the art, somelatexes will form films of unplasticized polymer, while others require aplasticizer to be film-forming. The nature and amount of any plisticizerrequired to render a latex film-forming will be known or may be easilydetermined by simple preliminary experiment. Likewise some latexes willform films by air drying while others require a short thermal fusion. I

The latex may be prepared by any of the known procedures forpolymerization in aqueous emulsion. Typically, the monomer is added toan aqueous solution of a polymerization catalyst such as potassiumpersulfate or hydrogen peroxide and a surface active agent capable ofemulsifying the monomers. Many suitable surface active agents are knownto the art. The polymerizable mixture is agitated to effectemulsification and polymerization is initiated by heating the emulsifiedmixture usually between 35 and C. The surface active agent is usuallyemployed in an amount corresponding to from 0.5 to 5 percent of theweight of the polymerizable organic compounds. The polymerizationcatalyst is usually added in an amount corresponding to from 0.5 to 5percent of the monomers. After polymerization is complete the resultinglatex is filtered and if necessary to make it film-forming, about 10percent plasticizer based on the weight of non-volatile solids in thelatex is thoroughly stirred into the latex. With those latexes which arenot good film-formers it is sometimes advantageous to add a small amountof a thickening agent to enhance their film-forming characteristics.Such thickening agents are usually hydrophilic colloids such as lowviscosity methyl cellulose or sodium alginate. It is a conventionalpractice in the latex'art to stabilize some latexes for storage orPatented Nov. 10, e

mechanical stability by the addition following polymerization of a smallamount of a wetting agent.

In preparing the new coating composition, the various inert ingredientsare initially mixed and ground together for several hours in a pebblemill, adding sufficient water to form a mixture of about 50 percentsolids content. By inert ingredients are meant those materials such assuspending pigments, dyes, fungicide or bactericides which may bedesired in the coating for an effect such as color or mildew proofing,not associated with the flame-resisLant characteristics of the coating.Examples of suitable suspending agents or dispersants are gumtragacanth, gum arabic, Irish moss and the like. Suitable well-knownsubstances to counteract the fermentation of the carbohydrate or proteincarbonific and the growth of fungi, are sodium pentachlorophenolate,beta-napthol, copper fluoride or other copper salts, boric acid, borax,zinc salts, fluorides, arsenates, arsenites and the like. To the pigmentslip so-formed from the inert ingredients may be added the spumific andcarbonific. is finally stirred in for a short time. A smooth stablecomposition containing about 50 percent total solids results. 2

The desired latex degree of intumescence and the area of surface char ofeach coating. The fire test consisted of exposing the coated surface ofa panel, inclined at an angle of 45 degrees, to the complete burning of1 cc. of absolute alcohol, the alcohol flame being focused on the boardat a point about 2 inches above the lower end of the panel. This firetest is described in Commercial Standard CS4249, U.S. Dept. of CommerceBulletin, Structural Fiber Insulating Board (4th ed). The amount ofprotection that each coating composition provides for each panel israted according to amount of intumescence and area of surface char.Maximum fire retardant qualities are shown by those coatings whichprovide excellent intumescence (maximum depth of foam after exposure toflame) and minimum area of surface char. In addition, a 4-inch by12-inch strip was cut from the uncharred portion of each of the coatedpanels and these were tested for scrub or abrasion resistance using theGardner Straight Line Scrub TesterModel 105 (obtained from the GardnerLaboratory Inc., Bethesda, Maryland) and using in conjunction therewitha 0.5 percent aqueous soap solution. The number of cycles required toexpose 10 percent of the panels surface was determined.

O=no intumescence; 1=very slight intumescence; 2=po0r intumescence;3=tair intumescence; 4=g00d intumescence; 5=exeellent intumescence.

2 Number of wet scrub cycles to expose 0f the boards surface.

The new coating composition, prepared in this manner may be applied toany combustible building material to impart fire-retardant propertiesand to provide the material with a coating that is suflicientlyresistant to abrasion to permit thorough washing without significantloss of the protective coating. The new composition may be applied byroller, brush, or spray application. When the coating is applied at themill Where the fiber-board is made, the coated article is usually driedby a heat treatment at a temperature of about C. to 200 C. A coatedboard prepared in this manner is fire-retardant and its coating issubstantially resistant to abrasion encountered in normal use or inwashing operations. In the appended drawing is illustrated a normallyflammable cellulosic building material such as fiber-board coated withthe fire-retardant intumescent coating of this invention.

As further illustration of the invention, the following examples areoffered in tabular form in which all parts are by Weight. All of thecompositions were made by the aforementioned procedure in which theinert ingredients Were ground in a pebble mill for 3 hours withsufficient Water to form a mixture of about percent solids content. Tothe resulting pigment slip containing the inert ingredients, 22 parts ofpentaerythritol, 56 parts of monoammonium phosphate, and 10 partsdicyandiamide were added with stirring. Subsequently, the latex wasadded and mixed with the other ingredients for 10 minutes.

Each of the compositions was sprayed evenly over the surface of 12-inchsquare panels inch thick) of low density, previously uncoated fibrouswall-board. The coated panels were dried at 158 F. for ten minutesfollowed by a 5-minute period at 302 F. The dry coated panels were thenaged 16 to 20 hours at 75 F. and 50 percent relative humidity. Thesepanels Were then exposed to flame in a standard fire test to determinethe The compositions of this invention can be seen to provide almost asgood fire retardant qualities as the comparative composition containingno latex. In addition, the compositions provide outstanding scrubresistance to the coatings.

We claim:

1. An intumescent coating composition comprising a 40 to percent aqueousdispersion of a mixture consisting of to percent of non-film formingintumescent solids and enough of an aqueous film forming latex ofpolystyrene to provide correspondingly from 30 to 15 percent of thepolymer solids, based on the total weight of solids present; saidintumescent solids consisting essentially of (1) a foam formingingredient selected from the group consisting of monoammonium phosphate,diammonium phosphate, phosphoric acid, ammonium sulfate, sulfamic acid,ammonium sulfamate, ammonium bromide, sodium tungstate, and sodiumborate; (2) from 10 to 70 percent, based on the Weight of the foamforming ingredient, of at least one polyhydric compound from the classconsisting of starch, the hexitols, the pentitols, and the mono-, anddi-tetritois, the amount of any starch employed being less than 15percent of the weight of said foam forming ingredient; and (3) not morethan 55 percent, based on the weight of the foam forming ingredient, ofan amino compound from the group consisting of glycine, urea, dimethylurea, guanyl urea, guanidine, and dicyandiamide.

2. The composition as claimed in claim the latex is one of about 50percent solids.

3. The composition as claimed in claim the organic nitrogen compound isurea.

4. The composition as claimed in claim 1, wherein the organic nitrogencompound is dicyandiamide.

5. The composition as claimed in claim 1, wherein the polyhydriccompound comprises monopentaerythritol.

1, wherein 1, wherein 5 6 6. The composition as claimed in claim 1,wherein the polyhydric compound comprises dipentaerythritol. 7. Thecomposition as claimed in claim 1, wherein the polyhydric compoundcomprises a mixture of starch and pentaerythritol.

8. As an article of manufacture, a normally combustible buildingmaterial coated with the dry abrasion resistant composition claimed inclaim 1 to render the article fire retardant.

9. A cellulosic building material coated with the composition claimed inclaim 1.

5 10. A fiber-board coated with the composition of claim 1.

No references cited.

1. AN INTUMESCENT COATING COMPOSITION COMPRISING A 40 TO 60 PERCENTAQUEOUS DISPERSION OF A MIXTURE CONSISTING OF 70 TO 85 PERCENT OFNON-FILM FORMING INTUMESCENT SOLIDS AND ENOUGH OF AN AQUEOUS FILMFORMING LATEX OF POLYSTYRENE TO PROVIDE CORRESPONDINGLY FROM 30 TO 15PERCENT OF THE POLYMER SOLIDS, BASED ON THE TOTAL WEIGHT OF SOLIDSPRESENT; SAID INTUMESCENT SOLIDS CONSISTING ESSENTIALLY OF (1) A FOAMFORMING INGREDIENT SELECTED FROM THE GROUP CONSISTING OF MONOAMMONIUMPHOSPHATE, DIAMMONIUM PHOSPHATE, PHOSPHORIC ACID, AMMONIUM SULFATE,SULFAMIC ACID, AMMONIUM SULFAMATE, AMMONIUM BROMIDE, SODIUM TUNGSTATE,AND SODIUM BORATE; (2) FROM 10 TO 70 PERCENT, BASED ON THE WEIGHT OF THEFOAM FORMING INGREDIENT, OF AT LEAST ONE POLYHYDRIC COMPOUND FROM THECLASS CONSISTING OF STARCH, THE HEXITOLS, THE PENTITOLS, AND THE MONO-,AND DI-TETRITOLS, THE AMOUNT OF ANY STARCH EMPLOYED BEING LESS THAN 15PERCENT OF THE WEIGHT OF SAID FOAM FORMING INGREDIENT; AND (3) NOT MORETHAN 55 PERCENT, BASED ON THE WEIGHT OF THE FOAM FORMING INGREDIENT, OFAN AMINO COMPOUND FROM THE GROUP CONSISTING OF GLYCINE, UREA, DIMETHYLUREA, GUANYL UREA, GUANIDINE, AND DICYANDIAMIDE.